There is currently a great demand for semiconductor devices which are both miniaturized and highly-functional. FCB mounting technology has been introduced as one solution to satisfy the demand.
Conventional techniques for FCB include forming a bonding terminal (for example, a solder bump) on the electrode of the mount portion such as a semiconductor chip, so as to mount the mount portion to a substrate (mounted portion) or another semiconductor chip, with the solder bump surface being directed downwards. The solder bump is heated to be in a molten state which covers the electrode surface on the substrate, and the alloy layer is formed from the metal used to form the electrode and the solder, thus bonding the electrodes on the first and second semiconductor chips.
The section between the metal used to form the electrode and the solder bump is required to be in the sufficiently liquid state in order to perform the bonding. Therefore, the process using a flux has been employed for maintaining the sufficient liquid state. In the aforementioned process, the electrodes of the first and the second semiconductor chips are temporarily bonded with the solder bump through thermocompression. Subsequently, an oxide film of the solder bump is eliminated using the flux to bring the section between the metal used to form the electrode and the solder bump into the liquid state so as to perform the bonding using the solder bump.
Unfortunately, the active constituent of the flux residue may cause corrosion in the alloy layer of the metal for forming the electrode and the solder, thus deteriorating the strength at the bonded portion between the electrodes. Additionally, the method requires the treatment of the cleaning solution for cleaning the flux.
Japanese Patent Application Publication No. JP-A-6-268028 proposes an alternate solution for the problem by disclosing a method for eliminating the oxide film on the electrode surface and the solder bump surface using a mixture of the gases N2 and H2 as a reducing gas instead of using a flux.
However, in the aforementioned method, the solder bump is heated up to the melting point of the solder or higher during the temporary bonding phase. When the solder bump temperature is maintained at a high temperature (e.g., around the solder melting point), oxidation of the solder bump is accelerated to deteriorate the liquid state of the section between the metal used to form the electrode and the solder, which may further deteriorate the strength of the bonded portion between the electrodes. The time required for heating and reductive reaction in the temporary bonding step is relatively long, thus causing an increase in cost.